When a person is involved in a distressing event, they may feel overwhelmed and their brain may be unable to process the information like a normal memory. The distressing memory seems to become frozen on a neurological level. When a person recalls the distressing memory, the person can re-experience what they saw, heard, smelt, tasted or felt, and this can be quite intense. Sometimes the memories are so distressing; the person tries to avoid thinking about the distressing event to avoid experiencing the distressing feelings.

Some find that the distressing memories come to mind when something reminds them of the distressing event, or sometimes the memories just seem to just pop into mind. The alternating left-right stimulation of the brain with eye movements, sounds or taps during EMDR, seems to stimulate the frozen or blocked information processing system.

In the process the distressing memories seem to lose their intensity, so that the memories are less distressing and seem more like 'ordinary' memories. The effect is believed to be similar to that which occurs naturally during REM sleep (Rapid Eye Movement) when your eyes rapidly move from side to side. EMDR helps reduce the distress of all the different kinds of memories, whether it was what you saw, heard, smelt, tasted, felt or thought.